CPA theory of diluted Heisenberg antiferromagnet with random first- and second-neighbour exchange bonds

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Abstract
Extending a recent work (ibid., vol.11, p.497 (1978)) on ferromagnets, a diluted Heisenberg antiferromagnet is studied which possesses both nearest and next-nearest neighbour exchange interactions. As in that work, the coherent potential approximation (CPA) is used and for generality the possibility that exchange bonds between any pair of interacting magnetic atoms may also be random is included. By examining the frequency moment conservation behaviour and the dependence of the Neel temperature on randomness, it is shown that the present CPA is exactly analogous to that given in the previous work for the ferromagnet and, moreover, possesses the same level of accuracy, i.e. to two leading orders in 1/z (where z is of the order of the coordination number). For a variety of cases, numerical results are presented for the coherent exchange integrals, the Neel temperature, the density of states and the magnetic response functions.

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